1. Field of the Invention
The present invention relates to a single-substrate-heat-treating apparatus for a semiconductor process system, and particularly, to a single-substrate-heat-treating apparatus for performing a reforming process for removing inorganic impurities contained in a thin film formed on a target substrate and for performing a crystallizing process for crystallizing the thin film. The term "semiconductor process" used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or an LCD (Liquid Crystal Display) substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Discussion of the Background
In the manufacturing process of a semiconductor device, a film forming process and a pattern etching process are repeatedly applied to a semiconductor wafer. The requirements for the film forming process have become stricter in recent years in accordance with increases in the density and in the degree of integration of the semiconductor devices. For example, a further decrease in thickness and higher insulating properties are required even for a very thin insulating film such as an insulating film included in a capacitor or a gate insulating film.
A silicon oxide film or a silicon nitride film is widely used as such an insulating film. However, a metal oxide film such as a tantalum oxide (Ta.sub.2 O.sub.5) film has come to be used in recent years as an insulating film exhibiting further improved insulating properties. Such a metal oxide film can be formed by an MOCVD (Metal Organic Chemical Vapor Deposition) method, in which an organometallic compound is gasified for deposition of the metal. The insulating properties of the metal oxide film can be further improved by applying a reforming process to the surface of the metal oxide film after deposition.
In the process of forming a tantalum oxide film, at first, an amorphous tantalum oxide film is deposited on a semiconductor wafer, using a CVD apparatus. Then, the wafer is transferred into a heat-treating apparatus for reformation, where the amorphous tantalum oxide film is subjected to a reforming process. Then, the wafer is transferred into a heat-treating apparatus for crystallization, where the tantalum oxide film is crystallized by means of annealing.
In the reforming process, the wafer having the tantalum oxide film formed thereon is put under an atmosphere of a reduced-pressure containing ozone. Ozone is irradiated with ultraviolet rays emitted from a mercury lamp so as to generate active oxygen atoms. The organic impurities having C--C bonds, etc. and contained in the tantalum oxide film are decomposed by the active oxygen atoms so as to be removed from the tantalum oxide film. As a result, the insulating properties of the tantalum oxide film are improved. The reforming process is carried out at a temperature lower than the crystallizing temperature, e.g., at about 425.degree. C., in order to allow the tantalum oxide film to maintain its amorphous state.
In the crystallizing process, the tantalum oxide film is heated within the heat-treating apparatus in the presence of O.sub.2 gas to a temperature higher than the crystallizing temperature, e.g., to about 700.degree. C. By this annealing process, the tantalum oxide film is crystallized and the density thereof is increased in the molecule level, with the result that the insulating properties of the tantalum oxide film are further improved.
Jpn. Pat. Appln. KOKAI Publication No. 10-79377 (U.S. pat. appln. Ser. No. 08/889,590) discloses a cluster-tool-type film forming system in which a CVD apparatus, a reforming apparatus and a crystallizing apparatus are connected to each other via a common transfer chamber. The cluster-tool-type film forming system allows the through-put to be increased.
The heat-treating apparatus for performing the reforming or crystallizing process is constituted as a single-substrate-treating type in which wafers are treated or processed one by one in a process chamber. The process chamber of the single-substrate-heat-treating apparatus has a side wall used in a cold wall state, and the periphery of a worktable tends to have a temperature lower than the center of the worktable, because the periphery of the worktable is closer to the side wall than the center of the worktable is, and radiates heat more than the center of the worktable does. As a result, the planar uniformity of the temperature on a wafer during a heat-treatment is lowered, and thus the planar uniformity of the process is also lowered.
Incidentally, a heat-treating apparatus of the type in which a process gas is supplied from a shower type, generally causes the process gas to be spouted downward from the shower head, flow diagonally downward and spread to the periphery of the wafer. Further, the process gas tends to increase its flowing speed at the periphery of the wafer and thus stays there for a shorter period of time. As a result, the density of the process gas becomes thin on the center and periphery of the wafer, and thus the processed amount on the center and periphery of the wafer is less than that on the intermediate portion of the wafer.
The above described problem is more unacceptable, with an increase in wafer size from 6 through 8 to 12 inches. Further, the above describe problem is common to all the heat-treatment including film deposition process, diffusion process, and the like, as well as the reforming process and the crystallizing process.